1. Field of the Invention
This invention relates to a device for the detection of the residual supply of a developer, which device is incorporated in an image forming device utilizing an electrophotographic process and adapted to effect the detection of the residual amount of a developer.
2. Description of the Prior Art
As new additions to the class of such image forming devices as electrophotographic copying machines and laser beam printers which electrophotographically form a toner image on a recording paper, image forming devices of the type so adapted as to have an image forming cartridge disposed inside the main body of an image forming device for the sake of miniaturizing the image forming device are being developed. The image forming cartridge is otherwise called an image cartridge or an image forming unit and is so configured as to have a photosensitive drum incorporated inside a casing made of resin. The developer to be supplied to the photosensitive drum is stored in a hopper which is formed as a section of the interior of the casing. When the amount of the developer stored in the hopper has wholly run out or has become scarce, the image forming cartridge is replaced with a fresh supply.
For the purpose of detecting the fact that the residual amount of the developer stored in the image forming cartridge has run out or has become scarce, the image forming device has incorporated therein a device for detecting the residual amount of the developer (as disclosed in Japanese Patent Laid-Open No. 2-126,273, for example). This device for detecting the residual amount of the developer operates by the method of light transmission and, therefore, has two transmission windows formed in the image forming cartridge. A light-emitting element is set in place near one of the two transmission windows and a light-receiving element near the other transmission window. The light from the light-emitting element advances through the transmission window on the light-emitting element side, passes the interior of the image forming cartridge, advances through the transmission window on the light-receiving element side, and reaches the light-receiving element.
Some of the existing devices for detecting the residual amount of a developer operate by the method of reflection of light. In the device for detecting the residual amount of a developer by the method of light reflection, a transmission window is formed in an image forming cartridge and a reflecting plate is provided inside a hopper. A light-emitting element and a light-receiving element are disposed near the transmission window. The light from the light-emitting element is advanced through the transmission window, made to illuminate the interior of the hopper, reflected by the reflecting plate, advanced again through the transmission window, and allowed to reach the light-receiving element.
For the sake of convenience of explanation, the transmission window on the light-emitting element side used in the device of detection operating by the method of light transmission and the transmission window used in the device of detection operating by the method of light reflection will be collectively referred to as a light transmitting member for passing the light from the light-emitting element and allowing it to reach the interior of the image forming cartridge. Likewise, the transmission window on the light-receiving element side in the device for detection operated by the method of light transmission and the reflecting plate in the device for detection operating by the method of light reflection will be collectively referred to as a light processing member for enabling the light projected inside the image-forming cartridge to reach the exterior of the image forming cartridge. Further, the light transmitting member and the light processing member will be collectively referred to as an optical member.
When the developer continues to adhere to the light transmitting member and the light processing member, the detection of the residual amount of the developer cannot be attained because the light path extending from the light-emitting element to the light-receiving element is blocked with the deposited developer. The device for detecting the residual amount of the developer, therefore, is provided with a cleaning member which is made of a flexible material such as a polyester film. This cleaning member sweeps the light transmitting member and the light processing member at a predetermined interval to deprive these members of the adhering developer.
While the residual amount of the developer in the image forming cartridge is amply large, the light-receiving element continues to assume an OFF state because the light path extending from the light-emitting element to the light-receiving element is blocked by the developer. When the developer is absent from the interior of the image forming cartridge, the light-receiving element assumes an ON state because the light from the light-emitting element is allowed to reach the light-receiving element. When the voltage level emitted from the light-receiving element is compared with the predetermined threshold level and found to surpass the threshold level, the device judges that the developer is running short and turns on a developer empty display to inform the operator of the fact that the residual amount of the developer has become scarce.
The conventional devices for detecting the residual amount of a developer which operate as described above have the following problems.
The developer stored in the hopper is agitated by a member having the shape of a vane and, therefore, the behavior of the developer in the fluid state inside the hopper is complicated. When the residual amount of the developer is judged to be running short simply because the voltage level of the light-receiving element has surpassed the threshold level, therefore, the residual amount of the developer which actually exists when the voltage level surpasses the threshold level is liable to vary from one image forming cartridge to another. This fact poses a problem of inconsistency of the accuracy for detecting the residual amount of a developer. Further, since the judgment that the residual amount of the developer has become small is formed when the voltage level of the light-receiving element surpasses the threshold level even once, the device is at a disadvantage in erroneously forming this judgment when the voltage level is compelled by the influence such as of noise to surpass the threshold level.
Besides the aforementioned cleaning member for cleaning the optical member, the device for detecting the residual amount of a developer is provided with a transporting member for stirring and transporting the developer inside the hopper and a drive member for driving the cleaning member and the transporting member. This drive member is formed of a rotary shaft which is rotationally driven by means of rotation transmitted thereto from a motor. This rotary shaft is set in place rotatably in the hopper. Like the cleaning member, the transporting member is generally made of a material having flexibility. The rotary shaft is provided with a supporting member disposed along the axial direction. The transporting member and the cleaning member are attached to this supporting member. In consequence of the rotation of the rotary shaft, the transporting member is deflected on account of the nature of its material and enabled to stir and convey the developer and the cleaning member is likewise deflected on account of the nature of its material and enabled to sweep the developer adhering to the light transmitting member and the light processing member. When the rotary shaft is rotated, the edge of the supporting member which elongates along the axial direction of the supporting member constitutes itself the point of force for imparting force to the flexible material.
Further, the practice of integrally forming the transporting member and the cleaning member by inserting cuts in one flexible material has been heretofore in vogue. The device for detecting the residual amount of a developer which has the transporting member and the cleaning member integrally formed with a flexible material as described above entails the following problems.
The aforementioned edge of the supporting member which functions as the point of force for imparting force to the flexible material is elongated in a planar form parallelly to the rotary shaft. To the transporting member and the cleaning member, therefore, the force of identical intensity will be transported. When the aforementioned edge of the supporting member is located at a position at which the transporting member is allowed to manifest the prescribed function of conveyance, the possibility arises that the cleaning member will fail to contact the light transmitting member and the light processing member strongly enough to obtain thorough removal of the developer adhering to these members. Particularly, since the detecting device which operates by the method of light reflection discriminates the shape of a reflecting plate, the position for fixation thereof, or the angle of fixation thereof on account of the construction of the device, it is liable to entail the possibility that the reflecting plate will escape being sufficiently cleaned. In this case, the idea of manufacturing a flexible material of large thickness into a transporting member and a cleaning member for the sake of enabling the cleaning member to manifest amply the function of cleaning may be conceived. When this idea is embodied, however, the disadvantage ensues that the noise which is produced when the transporting member in the process of stirring and transporting the developer is relieved of deflection becomes loud. When the flexible material is not given any change in thickness and the edge of the supporting member is located at a position at which the cleaning member is enabled to manifest the predetermined function of cleaning, however, the disadvantage arises that the load exerted by the developer on the transporting member unduly increases and the torque required in rotating the rotary shaft proportionately increases.
Further, in the conventional device for detecting the residual amount of a developer, a single cleaning member is used in sweeping the developer adhering to the light transmitting member and the light processing member. The detecting device which operates by the method of light reflection entails the possibility that when the cleaning member happens to part from the reflecting plate before it has completed sweeping the entire surface of the reflecting plate, the developer is left adhering in the form of lines on the reflecting plate and, as a result, the light from the light emitting element is not reflected by the reflecting plate even when the residual amount of the developer decreases below the prescribed level and the residual amount of the developer can no longer detected accurately. In the device of the conventional construction which utilizes a single cleaning member for the purpose of cleaning both the transmission window and the reflecting plate, therefore, the length of the cleaning member is set at a size which is enough for cleaning the entire surface of the transmission window and the entire surface of the reflecting plate. Likewise in the detecting device which operates by the method of light transmission, the length of the cleaning member is set at a size enough to sweep the entire surface of the transmission window on the light-emitting element side and the entire surface of the transmission window on the light-receiving element side.
When the light transmitting member and the light processing member are both cleaned by the use of a single cleaning member, the following problems are entailed.
In the detecting device which operates by the method of light reflection, since the light-emitting element and the light-receiving element are laid out on the transmission window side, the reflecting plate is restricted, for example, its shape, the position or the angle to be fixed inside the hopper. Further, as described above, the length of the cleaning member is set at a size which is enough for the purpose of cleaning the entire surface of the transmission window and the entire surface of the reflecting plate. Because of this length, the cleaning member possibly emits a harsh noise when it is advanced past the reflecting plate and is consequently relieved of deflection. The detecting device which operates by the method of light transmission allows certain freedom in deciding the shape of a pair of transmission windows, the positions for fixing them, and the angle of fixation thereof. Since the transmission windows are both cleaned by one and the same cleaning member after all, the possibility of the cleaning member likewise emitting a harsh noise arises, depending such as on the positions for fixing the transmission windows.
Since the developer barely adheres in the true sense of the word to the light processing member, feeble force suffices to sweep the adhering developer off the light processing member. In contrast, the developer piles up on the light transmitting member and, therefore, a fair amount of force is required to sweep the accumulated developer off the light transmitting member. When the cleaning member is made of a polyester film having a relatively large thickness for the purpose of enabling the developer on the light transmitting member to be infallibly swept off, the harsh noise which the cleaning member emits in the process of passing the light processing member unduly grows in volume because the light transmitting member and the light processing member are both cleaned with one and the same cleaning member. Conversely, when the cleaning member is made of a polyester film having a rather small thickness for the purpose of repressing the generation of the harsh noise, the possibility arises that the developer piled up on the light transmitting member will not be infallibly swept off and, as a result, the detection of the residual amount of the developer will not be made accurately.